This invention relates to a method and apparatus for automatically deploying a moored sensor array with a sufficient cable scope to survive the dynamic effects of waves and currents.
For hydrophone arrays deployed from surface vessels or aircraft, it is necessary that the mooring for the array be established automatically and that its cable length be adjusted for the depth of the ocean at the mooring site with sufficient scope (ratio of cable length to ocean depth) to permit ocean waves and currents to move the surface buoy about without parting the cable to the anchor below. The practice is to eject a container from a vessel or aircraft with the entire array, including the surface buoy and cable, stowed in the container. One end of the container is weighted with seawater batteries and additional ballast as necessary for the container to descend to the ocean floor. The other end of the container is closed by a deflated buoy. The cable pack and array are stowed between the batteries and the deflated buoy.
Following entry of the container into the ocean, a seawater battery is activated to fire a squib that releases compressed CO.sub.2 gas into the deflated buoy. This inflates the buoy, causing it to pop out of the container and rise to the ocean surface as the container continues to descend. Connected to the bottom of the buoy is an electronic package for receiving data from the hydrophone array to be deployed, and for transmitting the hydrophone data over the air. Transmission from the array to the buoy is through the anchoring cable payed out from a cable pack as the container descends to the ocean floor. Following impact at the ocean bottom, the cable must be locked and the hydrophone array package is released from the container. The array package consists of an inverted "bucket" partly filled with buoyant material and partly filled with the hydrophone array (sensors and cable) so packed as to be payed out as the bucket ascends. Once all of the hydrophone cable has been payed out, the bucket will float above the anchoring container, thus deploying the hydrophone array in a vertical position over the container. In some missions, a horizontal array may be required. That could be accomplished by providing some way for the float to gradually decrease its buoyancy as currents near the ocean floor carry the float away from the anchoring container. Techniques for locking up the cable are disclosed in U.S. Pat. No. 4,143,349, and techniques for causing the float to gradually decrease its buoyancy in order to deploy a horizontal array are disclosed in an application by the same inventor filed concurrently herewith.
A problem of automatically deploying vertical, or horizontal, hydrophone arrays, is to provide sufficient cable scope between the surface buoy and the anchoring container. The amount of scope necessary is a function of the ocean depth and environmental forces that have to be withstood by the cable. If only enough cable is payed out to reach the floor in a calm sea, a high sea could cause the cable to part, particularly if the high sea is accompanied by strong surface currents. Methods of assuring enough scope have usually relied on the dispensing of extra cable from a separate cable pack, usually located at the buoy, but then either all of this extra cable is payed out, or some preset amount is payed out according to the depth of the mooring location. It would, of course, be preferable to pay out only a preset amount, but that does create the problem of having to preset the amount. Another problem is to automatically eject the array package from the anchoring container only after sufficient cable scope has been provided and the cable has been locked up.